The following is a guest post by Karon Thackston. Karon Thackston is President of Marketing Words, a full-service copywriting & content agency that helps businesses convert better, rank higher and sell more. Since 1999, her company has contributed to the search engine and sales success of organizations including Gorton's Seafood, American Boating Association, Entertainment.com and hundreds of Amazon sellers, large and small. Karon is author of the popular ebook “Amazon Advantage: Product Listing Strategies to Boost Your Sales”.

It was February 3, 2016. Before this landmark date, Amazon restricted sellers to a total of 50 characters for each of five fields (a total of 250 characters) for search terms. On that fateful day in February, however, the gate was let down and sellers had the freedom to include up to 1,000 characters per each of five fields (a total of 5,000 characters).

While the initial reaction from most sellers was, “YAHOO!” I immediately knew this would be trouble. You see, wherever there is a limit, there are people who don’t see that as a stopping point, but rather a recommendation from the source. The vast number of sellers instantly thought Amazon was suggesting they should include 5,000 characters of keywords in these fields. Nothing could be further from the truth.

Others followed the mindset that if you could, you should. They proceeded to fill every single character with words that might even remotely apply to the product they were selling until they reached a total as close to 5,000 as possible.

To clarify: No! Amazon is NOT recommending that you fill all the space with as many keywords as possible.

No, Amazon is not recommending that just because you can include 5,000 characters or search terms, you should.

What does Amazon say about relevant search terms?

Why is that? What difference does it make? For one, it can be misleading to shoppers. If you were trying to buy a case for an iPhone 5 and the Amazon search results kept showing cases for Samsung phones or the iPhone 6, you’d get frustrated and leave. Amazon doesn’t want customers to leave … they want them to buy.

And that’s not all. Just as Amazon states above, it can affect your sales.

How Can Including More and/or Irrelevant Keywords Hurt My Amazon Conversion Rate?

Here’s an excellent example. A seller lists a square plastic lunch plate with lid for sale on Amazon. She believes that she should include any and every term that includes the phrase “plastic container” so she can get as many visitors to her product detail page as possible. In addition to obvious terms such as “plastic lunch plate,” the seller fills her search terms with words like “plastic cereal container” and “plastic bowl container.”

The problem is, she isn’t selling a plastic cereal container. Look at the difference. A lunch plate is flat and has sections for the entrée and side dishes. The lid is also flat and snaps on top. However, a plastic cereal container has a completely different shape. It’s tall (like a cereal box) and has a pour-spout lid. There’s no way a cereal container could be a substitute for a lunch plate.

If the seller ever got her lunch plate ranked for the cereal term, and it showed up in the search results, shoppers would take one look and think, “This isn’t a lunch plate. I can’t use this!” and click away. The more times visitors land on your product detail page and leave without buying, the lower your conversion rate will fall.

How Can Lower Conversions Damage My Amazon Search Rankings?

Because Amazon is in the business of selling, they pay attention to pages that don’t convert. If yours consistently has a low conversion rate, Amazon will gradually reduce your visibility in the search results. If your page continues to convert poorly, you will eventually lose all rankings — and that will be the death of your listing.

How Do I Choose Relevant Search Terms?

I have two tests for determining whether a keyphrase is relevant to a product.

Look on Amazon.com. Search for the term in question. Keeping with our plastic lunch plate example, we’d go to Amazon and type in “plastic cereal container.” If that plastic container looks like the same thing you’re selling, it’s probably a relevant term.

Ask the question “Could I substitute this for what I’m selling?” Would you be able to use a plastic cereal container in the same way you would use a plastic lunch plate? If not, the search term is probably not relevant.

Think of it this way: If you owned a men’s clothier that specialized in better-quality suits, would you try to attract guys who are looking for discount sportswear? No. Why? Because they would not be likely to buy what you have. Just because they are men and they wear clothes doesn’t mean they would want to spend a good deal of money on a suit.

Quantity Does NOT Supersede Quality

It is much better to have accurate, relevant keywords in your Amazon listing than to drive droves of traffic that take one look and bounce off the page without buying.

As with most other types of conversions, you’ll most likely see the 80/20 rule in effect, where 80% of your traffic comes from 20% of your keywords. I recommend that you test the remainder to see if they are helping or hurting your overall conversions. The ones that are doing you no good, or that are only bringing unqualified shoppers, should be deleted.

To put it bluntly: Be choosy. Only select search terms that apply to your specific product and the customers who will be shopping for it. I explain (in detail) how to do this and more when performing keyword research for Amazon in my Amazon Product Description Boot Camp.

In addition, you will watch over my shoulder as I walk you through the way my team and I create expert titles, enticing bullet points, and engaging descriptions for our Amazon clients. It’s all included in this 4-week video series, fully updated for 2016.